The invention relates to water beds, and more particularly to an improved water mattress construction wherein longitudinal side seams on the mattress are eliminated.
A water mattress construction is shown in U.S. Pat. No. 3,753,823. In such construction, the mattress is folded from an elongate vinyl sheet which is essentially double the length of the vinyl mattress, in such a way that there results one end with no seam, and an end and two sides each having a seam throughout their lengths. The four vertical corners also define seams, since the mattress is of a box-like three-dimensional shape rather than a flat shape prior to filling.
Most water mattresses heretofore produced are either folded and seamed in a manner similar to that shown in the above patent, or are of two-piece construction, with a single seam extending throughout the perimeter, being located about halfway up the sides and the ends of the mattress when it is filled. Most mattresses of the latter type construction are produced in a flat two-dimensional configuration so that only when filled with water do they assume a third dimension. The ends and sides tend to assume a tapered cigar shape, so that when such a mattress is filled in a rectangular frame, it only roughly conforms to the frame and wrinkles at its corners.
The types of water mattress construction discussed above, particularly that of the above cited patent employing lapped seams throughout, have resulted in a relatively high resistance to wear and seam leakage problems. However it has been found that the side seams of a water mattress can cause problems after a prolonged period of usage. When a water mattress fails and leakage occurs, the failure point is nearly always located on one of the side seams somewhere in the vicinity of one of the corners, e.g., between the corner itself and a distance of about 18 inches from the corner. It is believed that the reason for such failures is related to a repeated pattern of wrinkle formation in the vinyl material, wherein the wrinkles extend down from the upper surface of the mattress to the seam and often tend to remain in the material. The wrinkles are usually caused by persons sitting on the side of the mattress when the mattress is in its frame. Since the corners of the water mattress in its frame have less support than the sides, due to the fact that they are always drawn inwardly when weight is placed upon the mattress, the wrinkles generally tend to run from the position where the person sits outwardly toward the vicinity of the corner. If the sitting is repeated over a period of time, the wrinkling tends to follow a certain pattern. The repeated wrinkling pattern, taken together with the aging of the vinyl material and the gradual loss by evaporation of plasticizers therefrom, results in a fatiguing of the vinyl material and either separation or rupture of the material at the seam.